JPH11114534A - Special fly ash treatment method - Google Patents

Abstract

(57) [Summary] Special fly ash (pH 10.5 to 12.7, alkalinity) which cannot sufficiently remove heavy metals by conventional detoxification treatment among fly ash generated in waste incineration plants and the like 1000
The present invention provides a safe, reliable, and low-cost method for immobilizing heavy metals, which is effective for 灰 2200 mg / L and fly ash having an aluminum content of 2% by weight or more. The method includes a step of subjecting the special fly ash to a heat treatment at 40 to 200 ° C., preferably 60 to 120 ° C., and a step of adding and kneading a carbonate, a hydrogen carbonate or a carbon dioxide gas. And a method for immobilizing heavy metals such as a dithiocarbamic acid-based chelating agent and kneading.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heavy metal fixing agent, and more particularly, to a pH of 10.5 to 12.7 and an alkalinity of 100.
0-2200 mg / liter, blank Ca elution concentration 1
The present invention relates to a method for immobilizing heavy metals in fly ash having a specific content of 00 to 6000 mg / liter and an aluminum content of 2% by weight or more.

[0002]

2. Description of the Related Art Conventionally, heavy metals are eluted from ash remaining after incineration in a garbage incineration plant or the like, and secondary pollution may occur.
Detoxification treatments such as fixing a heavy metal as a chelate compound or stabilizing with a cement or the like have been added.

[0003]

However, among the fly ash, there are many fly ash in which the detoxification treatment of heavy metals is not sufficient. For example, there is a series of special fly ash in which the pH easily fluctuates, the elution amount of Pb ions is unstable, and the addition of a chelating agent increases the elution amount of heavy metals. Conventionally, these special fly ash can be distinguished only from the processing results, and it has been extremely difficult to take measures to detoxify the incineration fly ash, which tends to generate such special fly ash.

The present inventors have conducted intensive searches and found that these special fly ash have a pH of 10.5 to 12.7 and an alkalinity of 10
It was found that the fly ash had a concentration of 00 to 2200 mg / liter, a blank Ca elution concentration of 100 to 6000 mg / liter, and an aluminum content of 2% by weight or more.

It is believed that the special behavior of such special fly ash is due to the hydration reaction of aluminum ions contained in the fly ash. Has a stable pH due to its buffering action, becomes fly ash with a stable elution amount of heavy metals, and is easy to treat.

The present invention has been made in view of the above-described circumstances, and is safe and reliable for the above-mentioned special fly ash.
Another object of the present invention is to provide a low-cost method for fixing heavy metals.

[0007]

SUMMARY OF THE INVENTION The object of the present invention is that
It is a special fly ash whose H, alkalinity, blank Ca elution concentration and aluminum content are included in specific ranges.

The pH in the fly ash to be treated according to the present invention is as follows:
50 g of fly ash is placed in a 1 L PP container together with 500 mL of water, shaken at 5 ° C., 200 rpm at room temperature for 6 hours with a shaker at 200 rpm, and filtered by suction with a glass filter having a pore size of 1 μm to obtain a filtrate. The filtrate obtained by the method specified in Notification No. 13 was measured with a pH meter.

The alkalinity was measured by neutralization titration of sodium carbonate consumption (mg / liter) required to neutralize the fly ash eluate according to the elution test method specified by the Environment Agency Notification No. 13.

The concentration of the eluted blank Ca is determined by inductively coupled high frequency plasma spectroscopy (ICP) of the above fly ash eluate.
Was measured.

The aluminum content is 1.0% fly ash.
g was dissolved and diluted in 2.0 g of hot concentrated hydrochloric acid.
The concentration was measured by ICP in the same manner as the concentration.

Fly ash specified by the above physical properties is
The pH value is liable to fluctuate, and the elution amount of Pb ions is unstable, and the addition of a chelating agent conversely increases the elution amount of heavy metals.

[0013] The fly ash treatment method of the present invention comprises a step of adding water, carbonate, bicarbonate, or an aqueous solution of such a salt to the special fly ash and kneading it, or , Water and kneading after kneading.

Preferably, a compound such as dithiocarbamate is added during the kneading. More preferably, the kneaded material is heat-treated at 40 to 200C, preferably 60 to 120C.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail.
In the present invention, water is added to such special fly ash in an amount of about 20 to 50 g per 100 g of fly ash, and 1 to 100 g of fly ash.
Carbon dioxide or bicarbonate of about 20 g, preferably about 1 to 10 g, or 0.1 g to 1 g of carbon dioxide gas is added to 100 g of fly ash and kneaded.

Examples of the carbonate include sodium carbonate and potassium carbonate, and examples of the hydrogen carbonate include sodium hydrogen carbonate and potassium hydrogen carbonate. Of these, addition of sodium carbonate and sodium hydrogencarbonate is particularly preferred from the viewpoint of cost and the like.

In the present invention, it is also preferable to add and knead a dithiocarbamic acid-based chelating agent during the above addition / kneading treatment. The combined effect of the chelating agent not only helps fix the heavy metal in the special fly ash, but also in the fly ash of an actual garbage incineration plant having a large pH fluctuation, the heavy metal from the fly ash other than the object of the present invention. It is effective to prevent elution.

Examples of the dithiocarbamic acid-based chelating agent include dialkyldithiocarbamates such as sodium diethyldithiocarbamate and potassium diethyldithiocarbamate; sodium N, N ', N "-tris (dithiocarboxy) diethylenetriamine;
In a molecule such as N, N'-bis (dithiocarboxy) diethylenetriamine salt, a dithiocarbamoyl group (NC (=
S) Compounds having S) can be mentioned.

The amount of the dithiocarbamic acid-based chelating agent is preferably 0.1 to 5 g per 100 g of fly ash. In the present invention, cement can be added for the purpose of solidifying fly ash.

When the above kneaded material is subjected to a heat treatment, the fixing effect is further improved. That is, a heat treatment at 40 to 200 ° C, preferably 60 to 120 ° C is performed. 4 heat treatments
If the temperature is lower than 0 ° C., the immobilization effect will be poor. Conversely 2
If the temperature is higher than 00 ° C., there is an immobilization effect, but it is not practical.

[0021]

The present invention will be described in more detail with reference to the following examples. (Example 1) 100 g of A fly ash (special fly ash subject to the present invention: the composition analysis value is shown in Table 1), sodium carbonate 5.0
g and 40 g of water were put into a Hobart mixer and stirred for 3 minutes to obtain a kneaded mixture. This was put in a polycup and cured for one week, and then an eluate was obtained according to the dissolution test method of No. 13 of the Notification of the Environment Agency. The eluate had a pH of 11.7 and a Pb concentration of 0.
It was 29 mg / L.

Comparative Example 1 A fly ash 100 g and water 40
g was put into a Hobart mixer and stirred for 3 minutes to obtain a kneaded mixture. After putting this in a polycup for one week,
An eluate was obtained according to the dissolution test method of the Environmental Agency Notification No. 13. The eluate had a pH of 12.1 and a Pb concentration of 14 mg / L. In comparison with Example 1, it can be seen that the addition of 5.0 g of sodium carbonate in the fly ash A significantly reduces the Pb concentration.

Example 2 A fly ash 100 g and water 40
g was placed in a Hobart mixer and stirred for 2 minutes to obtain a fine granular kneaded product. This was put in a plastic bag, heat-sealed, and 0.75 L of carbon dioxide gas was injected. As a result, the carbon dioxide gas was absorbed in 1 to 2 minutes. After aging for one week with heat sealing, an eluate was obtained according to the dissolution test method of No. 13 of the Notification of the Environment Agency. The eluate was pH 9.9, Pb concentration 0.0
It was 2 mg / L. Compared with Comparative Example 1, by injecting 0.75 L of carbon dioxide gas into A fly ash,
It can be seen that the H and Pb concentrations are significantly reduced.

Example 3 An aqueous solution containing 100 g of fly ash A, 5.0 g of sodium carbonate, and 37% of sodium N, N ', N "-tris (dithiocarboxy) diethylenetriamine (hereinafter referred to as chelating agent S). ) 2.0g
Was added to a Hobart mixer and an aqueous solution diluted with 40 g of water was stirred for 3 minutes to obtain a rice cake-like kneaded product. This was put in a polycup and cured for one week, and then an eluate was obtained according to the dissolution test method of No. 13 of the Notification of the Environment Agency. The eluate was pH 11.4,
The Pb concentration was <0.01 mg / L. In comparison with Example 1, it is understood that Pb can be substantially removed by using the chelating agent S in addition to sodium carbonate.

Comparative Example 2 100 g of fly ash A, 3.0 g of chelating agent S and 40 g of water were put into a Hobart mixer and mixed.
After stirring for a minute, a kneaded product was obtained. This was put in a polycup and cured for one week, and then an eluate was obtained according to the dissolution test method of No. 13 of the Notification of the Environment Agency. The eluate had a pH of 12.1 and a Pb concentration of 13 mg / L. As shown in Comparative Example 2, when sodium carbonate was not present and only chelating agent S was added, Pb was immobilized only by curing at room temperature. I could not do it.

Example 4 100 g of fly ash A, 5.0 g of sodium carbonate and 40 g of water were put into a Hobart mixer.
The mixture was stirred for 3 minutes to obtain a kneaded mixture. This was put in a polycup and heated at 80 ° C. for 3 hours. After curing for one week, an eluate was obtained according to the dissolution test method of the Environmental Agency Notification No. 13 method.
The eluate had a pH of 11.7 and a Pb concentration of 0.1 mg / L.

(Comparative Example 3) Fly ash B (100 g of fly ash not subject to the present invention; the composition analysis value is shown in Table 1) and water 46
g was put into a Hobart mixer and stirred for 3 minutes to obtain a kneaded mixture. After putting this in a polycup for one week,
An eluate was obtained according to the dissolution test method of the Environmental Agency Notification No. 13. The eluate had a pH of 12.6 and a Pb concentration of 22 mg / L.

(Comparative Examples 4.5) 100 g of fly ash B, 10 g of sodium carbonate and 46 g of water were put into a Hobart mixer and stirred for 3 minutes to obtain a cake-like kneaded product. This was divided into two parts, each of which was placed in a plastic bag. The other was heated at 80 ° C. for 3 hours to obtain Comparative Example 5. After curing both samples for one week, eluates were obtained in accordance with the dissolution test method of No. 13 of the Notification of the Environment Agency. The eluate of Comparative Example 4 was pH12.
6. When the Pb concentration was 5.6 mg / L, the eluate of Comparative Example 5 was p
H12.5 and Pb concentration were 5.4 mg / L. B fly ash did not show a sufficient effect of sodium carbonate on Pb concentration, as was observed with A fly ash.

Comparative Example 6 Fly ash 100 g and water 46
g was placed in a Hobart mixer and stirred for 2 minutes to obtain a fine granular kneaded product. This was put in a plastic bag, heat-sealed, and 5.0 L of carbon dioxide gas was injected. As a result, the carbon dioxide gas was absorbed in 1 to 2 minutes. After aging for one week with heat sealing, an eluate was obtained according to the dissolution test method of No. 13 of the Notification of the Environment Agency. The eluate has a pH of 12.1 and a Pb concentration of 2.4.
mg / L. In the fly ash B, a sufficient effect of carbon dioxide gas on the Pb concentration as in the fly ash A was not observed.

Table 1 shows the compositional analysis values of fly ash A and fly ash used in Examples 1 to 4 and Comparative Examples 1 to 6 described above.
Table 2 collectively shows the experimental results of Comparative Examples 1 to 4 and Comparative Examples 1 to 6.

[0031]

[Table 1]

[0032]

[Table 2]

[0033]

As described above, the present invention provides an effective detoxifying treatment for a special fly ash having a composition that cannot sufficiently detoxify heavy metals in fly ash by the conventional treatment method. It provides a method. The treatment method of the present invention is a safe, easy and low-cost method for fixing heavy metals, and is particularly useful for detoxifying fly ash in incineration plants where special fly ash is likely to be generated.

Claims (10)

[Claims] (1) pH: 10.5 to 12.7, alkalinity: 10
A heavy metal immobilization method in fly ash having a concentration of 100 to 2200 mg / liter, a blank Ca elution concentration of 100 to 6000 mg / liter, and an aluminum content of 2% by weight or more. , 1-20
A method for immobilizing heavy metals in fly ash, comprising a step of adding and mixing by weight. 2. A pH of 10.5 to 12.7 and an alkalinity of 10
A method for immobilizing heavy metals in fly ash having a concentration of 00 to 2200 mg / liter, a blank Ca elution concentration of 100 to 6000 mg / liter, and an aluminum content of 2% by weight or more, wherein a carbonate or bicarbonate is added to the fly ash. A method for immobilizing heavy metals in fly ash, comprising: adding 1 to 20% by weight to fly ash and kneading the mixture; and subjecting the kneaded material to a heat treatment at 40 to 200 ° C. 3. A pH of 10.5 to 12.7 and an alkalinity of 10
A method for immobilizing heavy metals in fly ash having a concentration of 00 to 2200 mg / l, a blank Ca elution concentration of 100 to 6000 mg / l, and an aluminum content of 2% by weight or more, wherein carbon dioxide gas is added in an amount of 0.1 to 100 g of fly ash. A method for immobilizing heavy metals in fly ash, comprising a step of adding and mixing 1 to 1 liter. 4. pH 10.5-12.7, alkalinity 10
A method for immobilizing heavy metals in fly ash having a concentration of 00 to 2200 mg / l, a blank Ca elution concentration of 100 to 6000 mg / l, and an aluminum content of 2% by weight or more, wherein carbon dioxide gas is added to the fly ash and 100 g of fly ash is added. On the other hand, 0.1 ~
A method for immobilizing heavy metals in fly ash, comprising: adding 1 liter and kneading; and subjecting the kneaded material to a heat treatment at 40 to 200 ° C. 5. pH 10.5-12.7, alkalinity 10
A method for immobilizing heavy metals in fly ash having a concentration of 00 to 2200 mg / liter, a blank Ca elution concentration of 100 to 6000 mg / liter, and an aluminum content of 2% by weight or more, wherein a carbonate or bicarbonate is added to the fly ash. Fixing heavy metals in fly ash, comprising: adding 1 to 20% by weight to fly ash; and adding and kneading 0.1 to 5 g of a dithiocarbamic acid-based chelating agent to 100 g of fly ash. Treatment method. 6. A pH of 10.5 to 12.7 and an alkalinity of 10
A method for immobilizing heavy metals in fly ash having a concentration of 00 to 2200 mg / liter, a blank Ca elution concentration of 100 to 6000 mg / liter, and an aluminum content of 2% by weight or more, wherein a carbonate or bicarbonate is added to the fly ash. A step of adding 1 to 20% by weight to the fly ash, a step of adding 0.1 to 5 g of a dithiocarbamic acid-based chelating agent to 100 g of the fly ash, and kneading; and a step of adding 40 to 200 to the kneaded material. A method of fixing heavy metals in fly ash. 7. pH 10.5-12.7, alkalinity 10
A method for immobilizing heavy metals in fly ash having a concentration of 00 to 2200 mg / l, a blank Ca elution concentration of 100 to 6000 mg / l, and an aluminum content of 2% by weight or more, wherein carbon dioxide gas is added to the fly ash and 100 g of fly ash is added. On the other hand, 0.1 ~
A method for immobilizing heavy metals in fly ash, comprising: adding 1 liter and kneading; and adding and kneading 0.1 to 5 g of a dithiocarbamic acid-based chelating agent to 100 g of fly ash. 8. pH 10.5-12.7, alkalinity 10
A method for immobilizing heavy metals in fly ash having a concentration of 00 to 2200 mg / l, a blank Ca elution concentration of 100 to 6000 mg / l, and an aluminum content of 2% by weight or more, wherein carbon dioxide gas is added to the fly ash and 100 g of fly ash is added. On the other hand, 0.1 ~
Adding 1 liter and kneading; adding 0.1 to 5 g of a dithiocarbamic acid-based chelating agent to 100 g of fly ash; kneading; and subjecting the kneaded material to a heat treatment at 40 to 200 ° C. And a method for immobilizing heavy metals in fly ash. 9. The method for immobilizing heavy metals according to claim 1, wherein the carbonate is sodium carbonate. 10. The method for immobilizing heavy metals according to claim 1, wherein the bicarbonate is sodium bicarbonate.